A number of diseases and disorders in humans and other mammals are characterized by the build-up of excessive fluid pressure within one or more body cavities. In many instances, implantable devices or surgical procedures may be used to shunt excessive fluid from the body cavity wherein the excessive pressure build up is present, to one or more other sites within the body, as a means of receiving the undesirable pressure buildup, and thereby deterring the development of undesirable sequelae which may result from such pressure build-up.
i. Glaucoma
Glaucoma is a disease of the eye which is characterized by high intraocular pressure, and is among the leading causes of blindness in the world. In general, glaucoma results from a defect in the functional drainage system, whereby naturally occurring endogenous fluid (e.g., aqueous humor) is drained from the interior of the eye. The result of this decreased functional drainage of the eye is three-fold: a) increased intraocular pressure, b) degeneration of the optic nerve and supporting tissue at the optic nerve head (disk), and c) progressive loss of the visual field.
Individual cases of glaucoma are generally classified, on the basis of etiology, into two categories. These two major are "closed angle glaucoma" and "open angle glaucoma".
In closed angle glaucoma (syn. "angle-closure glaucoma", "narrow-angle glaucoma", "pupillary block glaucoma") excessive fluid accumulates within the anterior chamber of the eye due to the gradual closure of an anterior angle formed by the junction of the iris and the inner surface of the trabecular mesh work through which the aqueous humor is normally reabsorbed. Closure of this anatomical angle prevents normal drainage of aqueous humor from the anterior chamber of the eye.
In open angle glaucoma (syn. "chronic simple glaucoma" "simple glaucoma", "wide-angle glaucoma") the angle of the anterior chamber remains normal, but the drainage of aqueous humor from the anterior chamber is impeded or blocked by other means, such as edema or swelling of the trabecular spaces, abnormal pigment dispersion, or non-perforating injury to the eye resulting in vascular congestion.
Various pharmacologic modes of treatment have been used to lessen the intraocular fluid pressure in glaucoma patients. Drugs which have been administered to treat glaucoma have included parasympathomimetic agents of the choline ester type (e.g., bethanechol, carbachol and methacholine), carbonic anhydrase inhibitors (e.g., acetazolamide), anticholinesterase agents (e.g., physostigmine, pilocarpine, demecarium, echothiophate and isoflurophate), sympathomimetic agents (e.g, epinephrine, phenylephrine) and .beta.-adrenergic blocking agents (e.g., tymolol). However, these various drug therapies for glaucoma are sometimes associated with significant untoward effects, including headache, blurred vision, allergic reactions, retinal detachment, phacodinesis, histological changes within the eye and potential interactions with other drugs.
As an alternative to pharmacologic modes of therapy, at least some glaucoma patients may be treated surgically by creating surgical openings into the anterior chamber of the eye, to facilitate drainage of excess aqueous humor from the anterior chamber. Many of these surgical techniques involve the formation of an opening or hole into the anterior chamber, under the conjunctiva and/or scleral flap such that fluid will be drained by filtration from the anterior chamber of the eye, into the tissues located within the lateral wall of the eye. The major problems associated with these surgical filtration procedures stem from the size of the opening or hole made into the anterior chamber. These problems include hypotony, synechiae, inflammation, cataract, corneal decompensation (edema), vitritis, choroidal separation (detachment), macular edema, and infections which may cause endophthalmitis. Moreover, such glaucoma filtration surgery is often unsuccessful due to the formation of dense fibrovascular connective tissue (e.g., scar tissue) around the surgical opening formed into the anterior chamber. Such proliferation of connective tissue tends to close off the surgically-formed opening into the anterior chamber, thereby deterring or preventing the desired filtration of aqueous humor into the subconjunctival space.
In view of post-surgical complications associated with the development of fibrovascular connective tissue (e.g., scar tissue) around the surgical site, a number of implantable drainage devices have been used to ensure that the desired filtration and outflow of aqueous humor through the surgically-formed opening will continue, despite the formations of, scar tissue during the post operative period. Examples of implantable shunts or other implantable apparatus which have previously been implanted into the eye for drainage of aqueous humor from the anterior chamber of the eye include those described in U.S. Pat. Nos. 4,750,901 (Molteno), 5,041,081 (Odrich), 5,476,445 (Baerveldt), 4,886,488 (White), 5,454,796 (Krupin), 5,397,300 (Baerveldt), 5,372,577 (Ungerleider), 5,338,291 (Speckman, et al.), 5,300,020 (L'Esperance), 5,178,604 (Baerveldt, et al.), 5,171,213 (Price), 5,092,837 (Klein et al.), 4,968,296 (Klein et al.), 4,946,436 (Smith), 4,936,825 (Ungerleider), 4,886,488 (White), 4,806,382 (Burns et al.), 4,554,918 (White), 4,521,210 (Wong), 4,428,746 (Mendez), 4,184,491 (McGannon), 4,157,718 (Baehr), 4,030,480 (Meyer), 5,433,701 (Rubinstein), 5,346,464 (Camras), 5,073,163 (Lippman), 4,604,087 (Joseph), 5,180,362 (Worst), 5,520,631 (Li et al.).
The major disadvantage associated with the use of implantable shunts for treatment of glaucoma is that, in the immediate post operative period, the shunt may facilitate excessive fluid drainage which results in hypotony within the anterior chamber, flattening of the anterior chamber and potential choroidal detachment and/or phthisis bulbi. Such excessive post-operative fluid outflow may also result in expansion of the fibrous capsule located beneath the rectus muscles of the eye. Such expansion or the fibrous capsule can stretch and tighten the rectus muscles, thereby inducing heterotropia and impairing the motility of the eye in the quadrant wherein the implant is located. Additionally, due to the size of some of these shunt devices, the bulky presence of the device itself within the subconjunctival space can cause scleral erosion, changes in the natural curvature of the eye, or damage to adjacent vasculature and tissue. Other problems associated with the use of implantable shunt devices for the treatment of glaucoma involve friction and wear imparted by the implanted shunt device, irritation of the iris endothelium caused by insertion of the shunt device into the anterior chamber, and migration of microbes, cells, proteins or other matter through the lumen of the shunt device and into the anterior chamber of the eye.
Also, the surgical procedures used to implant the prior art fluid shunting devices have typically been laborious in nature and have typically required that suturing of the fluid shunting device to the surrounding tissue of the host, to hold the fluid shunting device at its desired location within the eye. The installation of sutures to anchor the implanted fluid shunting device is time consuming and, in cases where such sutures are not properly placed, can result in undesirable tugging, traction or stress on the surrounding tissue and/or disconfiguration of the implanted device. Also, the installation of such sutures can result in unintentional, iatrogenic perforation of the anterior or posterior chabber of the eye, with resultant leakage of aqueous or vitreous humor and/or resultant cellular ingrowth and opacification of the aqueous and/or vitreous humor.
ii. Hydrocephalus
Another disorder in which the build-up of abnormal fluid pressure is a hallmark is hydrocephalus. In hydrocephalus, excessive amounts of cerebrospinal fluids accumulate within skull, generally resulting in elevated intracranial pressure. The chronic elevation in intracranial pressure caused by such excessive cerebrospinal fluid within the skull typically results in enlargement of the head, prominence of the forehead, brain atrophy, mental deterioration, and convulsions. Hydrocephalus is maybe of congenital origin or may be an acquired disease. In some patients, hydrocephalus is of sudden onset while in others it is slowly progressive.
In addition to various pharmacologic therapies, the surgical approach to treatment of hydrocephalus often involves the implantation of a shunt which facilitates drainage of excess cerebrospinal fluid from the intracranial space, to other areas of the body wherein it can be tolerated-most often into the peritoneal cavity. In addition to glaucoma and hydrocephalus, numerous other diseases and disorders involve the buildup of excessive fluid within one or more anatomical spaces (i.e., cavities) of the body, and may be effectively treated by shunting of the excessive fluid from the affected body space (i.e., body cavity) to other region(s) of the body. However, in many cases, it is desirable that an implantable shunt device be used, and that such shunt device be valved or pressure-regulated such that only excessive fluid will be removed from the affected body cavity, while allowing the normal amount of such fluid to remain within the affected body cavity, so long as the pressure within the cavity is in the normal range. Thus, it is desirable for the implanted shunt device to include a pressure-sensitive opening or other pressure-actuated valving apparatus which will allow fluid to flow out of the affected body cavity only when the fluid within the body cavity has exceeded a predetermined maximum pressure.
One complication associated with the use of implantable shunt devices to drain fluid from body cavities is that proteins, cellular matter, or other debris may block the lumen of the shunt tube thereby interfering with the drainage of fluid through the tube. Also, proliferation of tissue or blebs may compress, collapse, or block the shunt tube. Moreover, pathogenic microorganism or irritating proteins or other matter may migrate through the lumen of the shunt tube into the affected body cavity in a manner which can lead to iatrogenic infection, irritation or inflammation of the affected body cavity.
Given the above-summarized limitations and drawbacks associated with the implantable fluid-shunting devices of the prior art, it is apparent that no single fluid-shunting device has proven to be optimal for all applications. Accordingly, there exists a need in the art for the development for new implantable fluid-shunting devices which include: a) means for valving or pressure-regulation of the fluid outflow, b) means for preventing microbes, proteins, cells or other matter from clogging the shunt or migrating through the shunt in to the affected body cavity and/or c) means for anchoring the fluid-shunting device in its desired implanted position, without the need for suturing of the device to the adjacent tissue.